The present invention relates to an alternate route to star-block formation in anionic polymerization involving the use of multifunctional initiators.
Highly branched block copolymers, sometimes called star-block copolymers, are known in the art of anionic polymerization. These star-block copolymers are prepared by first forming linear block polymers having an active lithium atom on one end of the polymer chain. These active, linear polymer chains are then coupled by the addition of a polyfunctional compound having at least three reactive sites capable of reacting with the carbon to lithium bond on the polymer chains to add the polymer chain onto the functional groups of the compound. In the case where the polyfunctional compound is divinylbenzene, the coupling reaction results in a star-block having several arms and a cluster of living anionic species at the nucleus of the star. It is at this point that the reactive star anions are terminated by reaction with proton active reagents, such as alcohols, to yield the final polymer.
Zelinski, U.S. Pat. No. 3,280,084, polymerized butadiene with butyllithium initiator to form B-Li blocks (where B is polybutadiene) which when couplied with 0.02 to 1 part by weight per 100 parts of monomers of divinylbenzene gave star-block copolymers having polydivinylbenzene nuclei and several identical arms of polybutadiene branching therefrom. The arms can also be either random or block copolymers of styrene and butadiene (from A-B-Li blocks, where A is polystyrene segment) where the diene is the major component.
Farrar, U.S. Pat. No. 3,644,322, teaches to make star-block copolymers having several arms wherein half of the arms are grown out from the multi-lithiated nucleus and then terminated.
Bean et al, U.S. Pat. No. 3,651,025, teaches the same procedure as Farrar, but forming different arms in the growth from the multi-lithiated nucleus.
Farrar, U.S. Pat. No. 3,787,510, is a division of U.S. Pat. No. 3,644,322 above, claiming the multilithium nucleus prior to growing the other half of the arms.
Crossland et al, U.S. Pat. No. 4,010,226, teaches to form star-block copolymers using divinylbenzene as coupling agent, growing new arms from this star-block copolymers, which arms are 5000 to 1,000,000 molecular Weight and then capping these longer arms at the extremities away from the nucleus with various reagents which react with the carbon-to-lithium bonds.